1. Field of the Invention
The invention relates generally to a process for pretreating cellulose-containing biomass materials, in particular lignocellulosic biomass materials.
2. Description of the Related Art
There is an interest in converting biomass materials to liquid fuels. In particular lignocellulosic biomass materials are attractive starting materials, as they are abundantly available and have no alternate use as food materials.
Gasification of biomass to syngas, followed by a Fischer-Tropsch process for converting syngas to liquid hydrocarbons, is one process being proposed for the conversion of biomass materials to liquid fuels. This approach is inherently inefficient, as gasification breaks down the biomass material to very small molecules, which then need to be built back up to larger ones. Moreover, gasification involves oxidation, which is directionally away from the formation of hydrocarbons.
Pyrolysis, in particular flash pyrolysis, is being studied as an alternate route to hydrocarbons from biomass. It has been found that short reaction times favor the formation of liquid reaction products, at the expense of gaseous reaction products.
Pyrolysis processes are hampered by the inherent stability of lignocellulose, which can be viewed as a composite of lignin, cellulose, and hemicellulose. Relatively severe reaction conditions are necessary in pyrolysis processes in order to open up the texture of the lignocellulose composites. Yet, these severe reaction conditions cause over-cracking of the primary pyrolysis products, resulting in high coke and gas yields.
Thus, there is a need for a pretreatment process in which the texture of the lignocellulose composite is opened-up, so that it can be converted in a subsequent process, such as a pyrolysis, under less severe conditions than those required for biomass material that has not been pretreated.
It has been known to dissolve cellulose in Ionic Liquids. S. Fischer et al., “Inorganic molten salts as solvents for cellulose”, Cellulose 10: 227-236, 2003, discloses the use of various molten salt systems as solvent media for cellulose. The aim is complete dissolution of the cellulose.
Sheldrake and Schleck, “Dicationic molten salts (ionic liquids) as re-usable media for the controlled pyrolysis of cellulose to anhydrosugars”, Green Chem. 2007, pp 1044-1046, reports on low temperature pyrolysis of cellulose in ionic liquid media. The starting material is pure cellulose. Pyrolysis is carried out with the cellulose in solution.
Thus, there is a need for a pretreatment process for cellulose-containing biomass materials, in particular lignocellulosic biomass materials.